[clang] [Clang] Improve diagnostic of Microsoft integer literals and refactor its truncation logic (PR #212743)

[Shengxin Pei via cfe-commits]

TPPPP72 wrote:

@frederick-vs-ja It looks like we might need to split this PR, given that the intended behavior isn't clearly defined yet. What do you think?

https://github.com/llvm/llvm-project/pull/212743